1. Field of the Invention
The present invention relates to a color image sensor and a color filter array which are applied to a color imaging unit such as an electronic camera and a video camera, and the color imaging unit.
2. Description of the Related Art
A color image sensor has been conventionally applied to a color imaging unit such as an electronic camera and a video camera.
In general, it is preferable for the color imaging unit to bring spectral sensitivity characteristics of its imaging optical system from a shooting lens to a color image sensor closer to spectral sensitivity characteristics of the eyes of a human being (or color matching functions which are publicly known) as much as possible.
The color image sensor has a G pixel detecting green light, a B pixel detecting blue light, and an R pixel detecting red light, which are arranged in an array state.
Especially, a Bayer matrix has the G pixels arranged in a checkered pattern and the B pixel and R pixel arranged alternately in gaps between the G pixels. That is, one unit (pixel block) is constituted of the four pixels made of the two G pixels, one B pixel, and one R pixel.
Incidentally, the reason why the number of the G pixels is greater than the R pixel and B pixel is as follows.
One of characteristics of the eyes of the human being is that the number of cells detecting green is greater than the number of cells detecting other colors. Accordingly, the eyes of the human being have wide detection luminance range of the green light.
Accordingly, when a large quantity of the G pixels are provided in the image sensor, it is possible to extend the detection luminance range (what is called dynamic range) similarly to the eyes of the human being.
Meanwhile, since color range to be discriminated by the three kinds of pixels, which are the R pixel, G pixel, and B pixel, is slightly narrower than the color range to be discriminated by the eyes of the human being, two different colors for the eyes of the human being are sometimes detected as the same color.
Therefore, a color image sensor of a multiband type in which another type of pixel is further added has been recently proposed (for example, a color image sensor described in Patent Document 1=Japanese Patent Application Laid-Open No. 2002-271804).
According to the color image sensor of the multiband type described in the Patent Document 1, a Y pixel detecting color between green and red (yellow) is added in addition to the R pixel, G pixel, and B pixel, to thereby enlarge detection color range.
However, according to the conventional color image sensor of the multiband type, it is necessary to reduce the number of the G pixels from two to one, in order to add the Y pixel into the pixel block. Therefore, there are tendencies that the detection luminance range of the green light is reduced and the detection luminance range of the color image sensor is reduced.
Incidentally, this problem is not caused when the color image sensor is changed to a multi-board type because the Y pixel can be added without reducing the number of the G pixels, but it is not so suitable for the electronic camera and video camera requiring downsizing, because an arrangement space is increased from the necessity for branching an optical path and arranging the image sensor for each branched path.
Further, this problem is not caused when a rotary switching filter is applied because the Y pixel can be added without reducing the number of the G pixels, but it is not so suitable for the electronic camera and video camera requiring downsizing, because the arrangement space is increased similarly to the case of the multi-board type.